I don't think it will come as a shock to anyone that the MobileMe transition hasn't gone as smoothly as Apple would have liked. A recent update to the .Mac support page (shown above) states, 'The MobileMe transition is underway but is taking longer than expected. Please refer to the official System Status to the right for current information on the availability of MobileMe services. We apologize for any inconvenience.'
Cory was able to sneak into MobileMe and take some pictures, so at least you can check out what you're missing. Here's hoping that this rocky start leads to a much more solid product since, as Mike pointed out, .Mac wasn't exactly a hallmark of uptime itself.